In the construction of buildings it is often necessary to provide an elevated platform alongside the building to enable work to be done on the building's exterior. Tubular frame scaffolding was developed for this purpose. Much effort has been put into the design of these types of scaffold to make them easy to transport and assemble. The scaffold arrives at the construction site in prefabricated U-shaped trusses. These trusses typically have two horizontal members connecting two pairs of spaced apart uprights, each pair of uprights having an inner and an outer vertical member. These trusses are inverted to form the vertical supports of the scaffold. The outer vertical member of each truss has an upper end portion of reduced diameter for insertion into the lower end portion of another truss, which allows the U-shaped trusses to be stacked into towers.
Cross braces connect the individual towers and provide lateral stability. When properly stabilized, scaffolds can be constructed which rise 10 stories or more above ground, without danger of collapse. Wooden boards may be placed across the upper horizontal members of two horizontally adjacent trusses to provide a work platform. This design enables work to be done at any level of the scaffolding. A scaffold can also be horizontally expanded by extending cross braces and work platforms from one truss to another ad infinitum. In this manner, a scaffold can be made to span an entire wall.
Without some form of fall prevention, scaffolds of this type would be extremely hazardous places to work since they are essentially open platforms. Some fall prevention mechanism is needed. Unfortunately, the methods most commonly used to protect workers from falling have not kept pace with scaffolding itself in terms of ease of transportation and assembly. Wire mesh screens are sometimes used but are time consuming and labor intensive to install. They are equally difficult to remove, and once removed are bulky to transport for disposal or reuse. If not reused, the consumption of wire mesh screens becomes costly.
Guard rails are another form of barrier to protect workers. Guard rails made of lumber are sometimes used but they are clumsy, not always sturdy, and must be wired into place--a time consuming process. Metal guard rails are sometimes used. They are more sturdy than wood rails or wire mesh, but typically must be clamped onto the scaffold. Clamps and their associated nuts and bolts are prone to being lost in the chaotic environment of a construction site.
In addition, whether the guard rails are wood or metal, they must be positioned an appropriate distance above the work platform to make them at all effective for fall prevention. At present, Federal and several state agencies have adopted rules that specify the location of guard rails on scaffold work platforms, mandating that rails be placed at heights of 21 inches and 42 inches above each work platform. These regulations make it increasingly important to provide guard rail assemblies which can be easily assembled and accurately positioned above a work platform.
One guard rail assembly is disclosed in U.S. Pat. No. 3,752,262 to Helms. The Helms assembly includes vertical posts which must be inserted over the free end of a truss, with the rails then being mounted between the posts by way of brackets which are premounted on the posts. Because it must be mounted over the free end of a truss, the Helms assembly can only be used above the uppermost platform and is not suitable for use with a multiplatform scaffold.
U.S. Pat. No. 4,782,914 to Nail also discloses a guard rail assembly but it is a complex and bulky system. The Nail system involves multiple cross-brace members and rails pivotally and slideably mounted to one another. The Nail device must be positioned by a U-shaped clamp that engages a rung included on the outer vertical member of some construction scaffold designs. Only one guard rail clamp can be properly positioned on each truss rung above a work platform and only one guard rail can be attached to each clamp. Consequently, the Nail device is ill suited for use on a work platform spanning three or more truss towers since two guard rails must be attached to the middle truss. In addition, location of the rail depends on the location of a truss rung which may or may not be a suitable location for compliance with regulations on for safety.
It would therefore be desirable to have a guard rail assembly which can be used above any intermediate platform of a multiplatform scaffold, which can locate the guard rails at one or more proper heights above a work platform, independently of locations of other scaffold parts and is economical to transport and assemble without the need for separate small pieces like nuts, bolts, and clamps that are easily lost in the chaotic environment of a construction site.